The present invention relates to a resist processing method and resist processing apparatus for coating and forming a thin film, such as a photoresist film, on a substrate such as a semiconductor wafer having an already formed circuit pattern with an uneven/stepped surface.
The photolithography process for manufacturing a semiconductor device includes coating a photoresist solution on the surface of a semiconductor wafer to form a resist film, baking this resist film, exposing the film with light with the use of a pattern and subjecting it to a develop-processing.
In the process of coating the photoresist film, use is made of the so-called spin-coating method by which the wafer, being spun, is supplied at its center surface area with a resist solution and the resist solution is diffused under a centrifugal force over a whole wafer surface. In the case where a resist solution is coated on an uneven/stepped surface of a wafer W with a circuit pattern layer 2 already formed thereon, a thickness tmin of a resist film 3 on a top area 2a becomes extremely smaller than a thickness tmax of the resist film on a bottom area 2b as shown in FIG. 1. If, therefore, in a subsequent light exposure step, the next circuit pattern is subjected to light exposure, there is a risk that there will arise a variation in the width of a light beam. Such a light beam width variation tendency emerges more prominently when the light exposure wavelength becomes short from an i line to a KrF excimer laser.
In recent times, the light beam width of a circuit pattern for the semiconductor device is more and more microminiaturized and there is a high demand that the thickness of the resist film be further reduced.
It is accordingly the object of the present invention to provide a resist processing method, comprising:
(a), to a substrate having a circuit pattern with an uneven surface formed thereon, coating a photoresist solution to, by doing so, form a photoresist film;
(b) subjecting the substrate to heat processing to chemically modify a portion of the photoresist film to, by doing so, create a modified resist layer of a substantially uniform thickness from the uneven surface of the circuit pattern; and
(c) removing only a resist layer unmodified at the step (b) to leave the modified resist layer on the uneven surface of the circuit pattern.
In the step (a), use can be made of, for example, a spin coating method. It is preferable that the thickness of the resist film 3 be made thicker than a conventional counterpart. It is preferable that the film thickness of the resist film 3 be variously set, in a range of 300 to 900 nm for instance, in accordance with the thickness of the pattern layer 2. Incidentally, the pattern layer 2 contains a source electrode, gate electrode, element isolation region, etc., and a high/low difference between the top 2a and the bottom 2b is as great as about 200 nm. And the thickness t5 of the modified layer 3a is required to be at least 100 nm. It is, therefore, necessary that an initial film thickness t4 from the bottom 2b be made as large as above 300 nm. If, on the other hand, the resist solution coating film 3 is extremely thicker, it takes too much time to remove the non-modified layer 3b. It is preferable that the initial film thickness t4 of the resist solution coating film 3 be made below 900 nm. It is to be noted that, for the resist, the thickness of the modified layer is set to be 500xc2x150 nm.
Further it is preferable to provide, before the step (a), an anti-reflection film forming step for covering the uneven surface of the circuit pattern with a hard-to-reflect bottom anti-reflection coating film. The anti-reflection film forming step preferably comprises the step (A) of coating a solution for an anti-reflection film to the uneven surface of the pattern, the step (B) of subjecting the substrate to heat processing to cause a portion of the anti-reflection film to be chemically modified to create a modified layer of a substantially uniformly thick anti-reflection film from the uneven surface of the pattern and the step (C) of removing only a layer unmodified at the step (B) to leave the modified layer on the uneven surface of the pattern. In this case it is preferable that the coating film thickness of the anti-reflection film be made thicker than a conventional thickness of 80 to 90 nm. More preferably, a film thickness from the bottom 2b be set to be 250 to 350 nm. Further, the thickness t5 of the modified layer is set to be 100xc2x120 nm for the anti-selection film.
Here, the term xe2x80x9cmodifiedxe2x80x9d is intended to mean that the coated resist film and anti-reflection film are changed or altered in their chemical property, such as the modified portion as distinct from the non-modified portion is not dissolvable in a specific chemical solvent or is strongly resistant to the ashing processing and etching processing.
An explanation will be given below about the heat processing for forming the resist""s modified layer 3a. 
When the substrate is heated from its rear surface side, heat is uniformly transmitted through the substrate. If any uneven or stepped surface is formed on the substrate surface, the heat thus transmitted through the substrate is transmitted past the uneven or stepped surface of the pattern uniformly into the resist film until it reaches a modified resist film portion of an intended predetermined depth. When this occurs, the heat processing is stopped so as to stop the transmission of the heat. By doing so, it is possible to form a modified layer and non-modified layer. Such heating temperature/heating time condition is properly set in accordance with the high/low difference of the uneven surface of the pattern.
It may also be considered that, since the photoresist is sensitive to temperature, heat is inadvertently transmitted through the resist film before the step (b) following the step (a) and it is not possible to create an intended modified layer and non-modified layer. For this reason, heating is done from the rear surface (lower surface) side of the substrate and cooling is made from the upper side of the substrate, so that it is possible to prevent the suppression of the heat transmission rate as well as the progress of an inadvertent heat transmission and consequent failure of desired unmodified and modified layers to be created. That is, according to the present invention it is possible to control the transmission of the heat and ensure the easiness with which any desired modified and non-modified layers are created.
As set out above, if subsequent to the creation of the modified and non-modified layers the non-modified layer is removed, then the modified layer (resist film) of the same thickness is left on the top 2a and bottom 2b of the pattern in a manner to follow the uneven surface of the pattern as shown in FIG. 8E.
As a solution for removing the non-modified layer 3b, use is preferably made of an organic solvent, such as a thinner. Further, the non-modified layer 3b may also be removed using a developing solution, an IPA (isopropyl alcohol) or other not-too-high-dissolution organic solvent as the dissolving solution. The non-modified layer may be removed by the ashing processing.
It is preferable to smooth the surface (surface portion) of the resist""s modified layer flat by subjecting the substrate to heating processing after the step (c) as already set out above. This is because, if the resist film has the uneven surface, there is a risk that the exposure light will be scattered on the uneven surface.
It is desirable that, in the above-mentioned step (b), the photoresist solution coating film be heated from the rear surface side of the substrate, while cooling the photoresist solution coating film from an upper surface side of the substrate. By cooling the upper surface side of the substrate the upper layer (surface layer) of the resist film is not modified and only the lower layer (bottom layer) is modified.
In the above-mentioned step (b), the substrate is placed on the stage in a way to be partially supported only at its marginal edge portion in a contacting state and a heat energy radiation is emitted from the stage side toward the rear surface of the substrate. For this reason, a resistance heat generation heater is embedded in the substrate placing stage to use such a heat energy radiation means (heating means). It is to be noted that as the heating means use may be made of an infrared radiation heater.
Further, in the step (b), the radiation cooling plate may be moved nearer the upper surface side of the substrate to subject the photoresist solution coating film to radiation cooling or a cooling gas may be fed to the upper surface side of the substrate to cool the photoresist solution coating film.
A resist processing apparatus according to the present invention comprises a processing chamber, a stage provided in the processing chamber and supporting a substrate having a circuit pattern with an uneven surface formed thereon, a heating mechanism for heating the substrate on the stage from a rear surface side of the substrate, and a cooling mechanism for cooling the substrate on the stage from the upper surface side of the substrate.
According to the resist processing device, the substrate is heated on the rear surface (lower surface) side of the substrate with the substrate placed on the stage while cooling the upper surface side of the substrate. It is, therefore, possible to prevent the suppression of a heat transmission rate from the rear surface (lower surface) as well as the progress of an inadvertent heat transmission.
The heating mechanism can be realized by either incorporating a heat generation element in the stage or incorporating a heat exchanger in the stage through which a heat fluid passes. On the other hand, the cooling mechanism may be constructed by either locating a cooling plate just opposite to the stage to pass a coolant through the cooling plate or using electronic cooling members utilizing a peltier effect. Further, it may be possible to blow, against the photoresist layer, a chemically hard-to-react substance, for example an inert gas such as N2 gas, argon gas or helium gas.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinbefore.